Electro-hydraulic brake system with electronic pedal simulation

Abstract

This invention relates to an electro-hydraulic brake-by-wire system including a hydraulic pump and a plurality of valves to achieve a demanded braking force, and to achieve a desired brake pedal feel. The brake system includes a plurality of wheel brakes, a reservoir of hydraulic fluid, and a pump for selectively pumping hydraulic fluid from the reservoir and supplying pressurized hydraulic fluid to the wheel brakes for applying a braking force. The pump acts as a source of pressurized hydraulic fluid to the wheel brakes during normal brake apply, as well as during advanced braking functions as Antilock Braking (ABS), Traction Control (TC), or Vehicle Stability Control (VSC). An apply valve is associated with each of the wheel brakes for selectively permitting flow of pressurized hydraulic fluid from the pump to the associated wheel brake. A dump valve is associated with each of the wheel brakes for selectively permitting flow of pressurized hydraulic fluid from the associated wheel brake to the reservoir. A master cylinder is operated by a brake pedal for pressurizing hydraulic fluid. An isolation valve is associated with each of the wheel brakes for selectively preventing flow of pressurized hydraulic fluid from the master cylinder to the associated wheel brake. A sensor senses the position of the brake pedal and generates a pedal position signal representative of the position of the brake pedal. An electronic control unit receives the pedal position signal, which signal is utilized to determine a brake demand. The electronic control unit controls the operation of the pump, and the apply, dump, and isolation valves associated with each wheel brake to achieve a desired braking force at each wheel brake based on the brake demand and to regulate pressure generated by the master cylinder to achieve a predetermined relationship between the pressure generated by the master cylinder and the position of the brake pedal, whereby a desired pedal feel is achieved.

What is claimed is:  
     
       1. An electro-hydraulic brake system comprising: 
       a wheel brake;  
       a reservoir of hydraulic fluid;  
       a pump for selectively pumping hydraulic fluid from said reservoir and supplying pressurized hydraulic fluid to said wheel brake for applying a braking force during normal brake apply;  
       an apply valve in fluid communication with said wheel brake for selectively permitting flow of pressurized hydraulic fluid from said pump to said wheel brake;  
       a dump valve in fluid communication with said wheel brake for selectively permitting flow of pressurized hydraulic fluid from said wheel brake to said reservoir;  
       a brake pedal;  
       a master cylinder operated by said brake pedal for pressurizing hydraulic fluid;  
       an isolation valve in fluid communication with said wheel brake for selectively permitting flow of pressurized hydraulic fluid from said master cylinder to said wheel brake;  
       a sensor sensing the position of said brake pedal and generating a pedal position signal representative of the position of said brake pedal; and  
       an electronic control unit for receiving said pedal position signal, said pedal position signal being utilized to determine a brake demand, said electronic control unit controlling the operation of said pump, and said apply, dump, and isolation valves to achieve a desired braking force at said wheel brake based on said brake demand and to regulate pressure generated by said master cylinder to achieve a predetermined relationship between pressure generated by said master cylinder and position of said brake pedal, whereby a desired pedal feel is achieved substantially continuously during brake apply.  
     
     
       2. The brake system of claim  1 , wherein said isolation valve is a binary solenoid valve. 
     
     
       3. The brake system of claim  1 , wherein said apply isolation valve is a proportional pressure differential solenoid valve. 
     
     
       4. The brake system of claim  1 , wherein said dump valve is a proportional relief solenoid valve. 
     
     
       5. A brake system comprising: 
       a brake pedal;  
       a position transducer operatively connected to said brake pedal for generating a continuous brake position signal representative of the position of said brake pedal, proportionate to the travel of said brake pedal;  
       a master cylinder being selectively actuated by said brake pedal;  
       a wheel brake;  
       a conduit in fluid communication with said master cylinder and said wheel brake;  
       a pressure transducer for sensing the pressure within said conduit, said pressure transducer generating a pressure signal representative of the pressure within said conduit;  
       an isolation valve for selectively preventing fluid flow between said master cylinder and said wheel brake;  
       a source of pressure for supplying high pressure fluid to said wheel brake, said source being in fluid communication with said wheel brake and said conduit;  
       an apply valve for selectively regulating the pressure of the hydraulic fluid supplied to said wheel brake from said source;  
       a dump valve for selectively relieving the pressure at said wheel brake; and  
       an ECU for electrically controlling said isolation valve, said apply valve, and said dump valve in response to a comparison of said position signal and said pressure signal.  
     
     
       6. The brake system of claim  5 , wherein said apply valve includes: 
       a housing having an inlet and an outlet;  
       an armature movably mounted in said housing;  
       a valve seat fixed in said housing, said valve seat having an opening therethrough in fluid communication with said inlet;  
       a valve disk on said armature, said valve disk disposed adjacent said opening in said valve seat, wherein the position of said valve disk relative to said opening in said valve seat regulates the flow of fluid from said inlet to said outlet;  
       a spring biasing said armature so that said valve disk is biased against said valve seat to block said opening in said valve seat; and  
       an electrical coil positioned around said armature, said coil exerting a selectively variable magnetic force on said armature urging said armature to move away from said valve seat and compress said spring.  
     
     
       7. The brake system of claim  5 , further including: 
       a hydraulic cylinder having first and second ports, said first port being in fluid communication with said master cylinder;  
       a proportional control solenoid valve having an inlet port and an outlet port, said inlet port being in fluid communication with said second port of said hydraulic cylinder, said outlet port being in fluid communication with an isolation valve; and  
       a check valve for preventing fluid from entering said second port of said hydraulic cylinder from said master cylinder;  
       said ECU electrically controlling said isolation valve, said apply valve, said dump valve, and said proportional control solenoid valve in response to said position signal and said pressure signal.  
     
     
       8. The brake system of claim  5 , further including a proportional boost valve for selectively applying fluid pressure to said conduit, said ECU electrically controlling said isolation valve, said apply valve, said dump valve, and said proportional boost valve in response to said position signal and said pressure signal. 
     
     
       9. The brake system of claim  8 , further including a check valve for preventing fluid flow in a direction from said master cylinder to said proportional boost valve. 
     
     
       10. The brake system of claim  5 , wherein said source of pressure also supplies high pressure fluid to said master cylinder, thereby assisting said master cylinder in supplying pressure to said wheel brake, the brake system further including: 
       a proportional boost valve for selectively regulating the pressure of the hydraulic fluid from said source;  
       a feedback valve for selectively regulating the pressure of the hydraulic fluid supplied to said master cylinder from said source; and  
       a check valve for preventing fluid flow in a direction from said master cylinder to said proportional boost valve.